Method To Quantify Viscosity Effects on Dispersion Test Improves Testing of Drilling-Fluid Polymers
- A.H. Hale (Shell Development Co.)
- Document ID
- Society of Petroleum Engineers
- SPE Drilling Engineering
- Publication Date
- March 1991
- Document Type
- Journal Paper
- 44 - 50
- 1991. Society of Petroleum Engineers
- 4.3.1 Hydrates, 1.11 Drilling Fluids and Materials, 4.1.5 Processing Equipment, 4.1.2 Separation and Treating, 1.6 Drilling Operations
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- 259 since 2007
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Many of the available polymers are claimed to inhibit cutti-ngs dispersion effectively. The experiments done to support these claims show the effectiveness of the polymers in inhibiting dispersion of sized shale through the hot rolling dispersion test. One of the most significant factors in this test is the viscosity of the test fluid. The fluid viscosity can create the illusion that a particular product effectively bits cuttings dispersion. A method is particular product effectively bits cuttings dispersion. A method is presented in which the dispersion-inhibiting effect of viscosity can presented in which the dispersion-inhibiting effect of viscosity can be subtracted from the amount of shale to obtain a more accurate determination of the effectiveness of a drilling-fluid additive the inhibit cuttings dispersion. A comparison is presented that clearly demonstrates that the partially hydrolyzed polyacrylamide (PHPA) polymer is the best available polymer to inhibit cuttings dispersion polymer is the best available polymer to inhibit cuttings dispersion cost-effectively.
One of the major problems in studying the effects of drilling fluids on shales is the lack of a quick, inexpensive test. Chenevert and Osisanya extensively reviewed current methods for testing and characterizing shales and proposed new methods for doing some of these tests at the rig site. Other tests have been devised that either attempt to simulate downhole conditions or attempt to gather data about the molecular interactions of drilling-fluid additives and shale. These tests usually require sophisticated equipment and conditions and have positive and negative attributes, with the interpre-tation more or less left to the investigators and their biases. Although many tests are available, the most commonly run test in service and operator laboratories is the hot rolling dispersion test developed by Amoco and studied extensively by others. The test is easily run with a minimum amount of equipment and shale. Multiple comparisons can be done in a relatively short time. These ad-vantages have made the test popular.
Although the hot rolling test has advantages, the test also has many limitations. The limitations are centered around the equipment, the rock, and the test fluid. The principal factor for equipment is the oven. Variation in temperature can be a factor; however, the principal error observed in our laboratory is the difference in principal error observed in our laboratory is the difference in rolling rate between ovens. These differences can result is significant error ( >20 %). For comparison purposes, we do all of our testing in one oven or in ovens with comparable rolling rates.
The heterogeneity of the rock is a critical problem. A given shale type will vary not only in composition and exchange capacity but also in strength. Our strategy, when possible, is to do all our testing with one shale sample that is ground and mixed before any testing is done. This increases reproducibility and improves relative comparisons between test solutions.
In our testing, the shale is sized between 6 and 10 mesh. A composite sample is used for the test comparisons under identical water contents. After preparation of the test fluid, each sample to be tested is screened again to ensure that no disintegration of the sized shale occurred during storage. This has a significant impact on the reproducibility of our results.
As Beihoffer et al show, the water content can significantly affect the results. Our work* also has shown that the water content is critical to the observed dispersion rate. Controlling the native water content, however, is difficult, especially during the grinding process. In our laboratory, we use native cored shale with its process. In our laboratory, we use native cored shale with its native water content if possible; however, many samples we receive have already been exposed to air. Two approaches can be taken: we can try to reconstitute the shale with a presumed native water content, or we can allow the sample to air dry and then stabilize the shale to a specified water activity (for our laboratory, usually 30%). Our choice depends on time and what we know about the shale. We never oven dry because this can significantly alter the rock. Whatever the approach, the water contents for all the test samples for a given shale are always identical.
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